How to use a soldering gun

Soldering, bonds a metal junction such as two wires, by coating the surface of the joint with a metal alloy called solder. Solder is usually an alloy of tin and lead. Its melting point is varies with the mixture, but the most common alloys melt between 360 and 460 degrees Fahrenheit (185 – 240 C). It is interesting to note that solder melts at a temperature lower than the melting point of either lead or tin. There are three common tools used to heat the joint, they are: propane torches, soldering irons, and soldering guns.

Where a lot of heat is required, such as in soldering copper pipes in plumbing, a propane torch is used. For smaller jobs there is a wide range of electric soldering irons available. They are usually rated by their electrical power requirement in watts, with typical home soldering irons ranging from 30 to 100 watts. A soldering iron takes about 5 minutes to heat up to its working temperature and somewhat longer to cool to a safe storage temperature.

Finally there is the electric soldering gun. Where soldering irons have a heating element that heats a copper or alloy tip; in a soldering gun, the tip is also the heating element. Most soldering guns are hot enough to solder in less than 5 seconds and cool enough to touch in less than a minute. Soldering guns are ideal for the typical home electrical job like connecting speakers or installing automotive accessories. These jobs often have only a few connections to solder so a soldering gun can be a real time saver.

Probably the best choice is a dual heat model in the 100 to 200 watt range. The soldering tips are easily changed and there are a few specialized tips available for many models. Some tip choices are a normal tip for most jobs, a small tip for low temperature work such as repairing jewelry, a tip for heat cutting and sealing nylon rope, and a tip that is round and flat for sealing or repairing cracks in plastic. When metals such as copper wire are heated, they quickly form a layer of oxidation. This prevents the solder from adhering to the joint and causes a poor connection that is often intermittent and sometimes won’t even conduct a current at all!

To prevent this oxidation, a chemical called “flux” is used. Plumbers use an acid based paste or liquid flux. In electrical work, NEVER use any type of paste or liquid flux. They are usually electrically conductive and will cause short circuits, and they’re corrosive, too, and will eventually eat away the wires and terminals. The only safe flux is rosin flux which is incorporated into solder. The best solder to buy is 64/40 alloy, rosin core, and it must be marked that it is suitable for electrical work.

For normal electrical work 60/40 rosin core solder is recommended. The most common cause of problems in home electric and electronic projects is poor solder joints. By following a few simple rules, you can make solid, dependable solder joints.

Precautions: Solder is hot, and hot solder can flow like water. Start with a clean soldering tip. If it’s a new tip, use sandpaper or steel wool so the metal shines. With an old tip, you may need to use a file to remove badly oxidized areas. Once the tip is clean and shiny, press the soldering gun trigger to high and as soon as it’s hot, apply a coating of solder to the tip. Use a rag to spread the solder evenly over the tip. The materials to be joined must be clean, dry, and free of grease and oil. Use a wire brush or fine sandpaper to get the surfaces clean and shiny. Make a good mechanical joint. Crimp terminals with a crimping tool or pliers, and twist wires together tightly.

The correct way to solder the joint is to use the soldering gun to heat the joint until it is hot enough to melt the solder. Press the heated soldering tip to the joint, and then touch the solder to the junction of the soldering tip and the metals to be joined. When the joint is hot enough, the solder will flow over the surface of the metals and into the crevices around the joint. Once the joint is covered with a thin layer of solder, lift the solder and gun tip away from the joint and allow it to cool.

It is very important that the cooling joint not be disturbed. If it is moved while cooling you may end up with what is called a “cold solder joint.” A cold solder joint is physically weak and often a poor conductor. You can often spot one by its dull, sometimes grainy appearance. If this happens, use your soldering gun to reheat the joint until the solder completely melts, then let it cool.

Once you have completed your last joint, you can put the soldering gun back into your toolbox immediately because the tip cools very fast. Remember: Clean the joint, use a clean soldering tip, always use rosin core solder, the joint must be hot enough to melt the solder, and do not disturb the joint while it is cooling.

Although soldering is not difficult to master, it does take some practice. Once you’ve selected and purchased your soldering gun, be sure to try a few practice joints before using it on an important repair.

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